1. Field of the Invention
The present invention relates to a transient control of a spark ignited internal combustion engine during a switch between different combustion types.
2. Acronyms
The written description provided herein contains acronyms, which refer, for example, to combustion types, which may be selectively employed by a spark ignited internal combustion engine. For purposes of the written description herein, acronyms will be defined as follows:
Stratified Stoichiometric Charge Combustion (S.S.C.C.); this is a combustion type wherein, within a cylinder charge created in each combustion chamber, a relatively rich air/fuel mixture portion is locally created around a spark plug within the surrounding or background relatively lean air/fuel mixture under a condition that the overall air/fuel ratio of the cylinder charge is kept within a limited narrow window around the stoichiometry, and the relatively rich air/fuel mixture is ignited by a spark:
Stratified Stoichiometric Charge Combustion by Split Injection [S.S.C.C. (SPLIT)]; this is the species of S.S.C.C., wherein a split injection is performed to create the stratification of the cylinder charge:
Stratified Lean Charge Combustion (S.L.C.C.); this is a combustion type wherein, within a cylinder charge, a relatively rich air/fuel mixture is locally created around a spark plug within the surrounding or background very lean air/fuel mixture under a condition that the over all air/fuel ratio of the cylinder charge is considerably greater than the stoichiometry, and the relatively rich air/fuel mixture is ignited by a spark:
Homogeneous Charge Combustion (H.C.C.); this is a combustion type wherein, within a cylinder, a homogeneous air/fuel mixture is created and ignited by a spark:
Homogeneous Stoichiometric Charge Combustion (H.S.C.C.); this is a combustion type wherein, within a cylinder, a homogeneous stoichiometric air/fuel mixture is created and ignited by a spark.
Homogeneous Charge Combustion by Single Injection [H.C.C. (SINGLE)]; this is the species of H.C.C., wherein a single injection is performed to create the homogeneous air/fuel mixture within a cylinder:
3. Description of Related Art
Recently, direct fuel injection is used to perform split injection for each engine cycle to achieve stratified charge for reduction of hydrocarbon emissions and catalyst warm-up time. For example, Nishijima et al. in U.S. Pat. No. 6,044,642 (=JP-A 10-212987) entitled xe2x80x9cDirect Fuel Injection Devicexe2x80x9d describes an engine which utilizes direct fuel injection and which employs a control strategy to increase the temperature of catalyst converter if it is found to be lower than a predetermined temperature. According to the control strategy, split injection is performed to create, in each combustion chamber, rich or stoichiometry mixture around a spark plug within the surrounding lean mixture and the spark timing is retarded to increase the temperature of exhaust gas. Split injection consists of injecting a first quantity of fuel for each engine cycle during the intake stroke and injecting a second quantity of fuel later in the same engine cycle during the compression stroke.
Tomita et al. in EP 0 943 793 A2, entitled xe2x80x9cControl for direct fuel injection spark ignition internal combustion enginexe2x80x9d published Sep. 22, 1999 filed by the assignee of the present invention describes an internal combustion engine. The engine employs fuel injectors positioned to directly inject fuel into combustion chambers, and an electronic engine controller (EEC) to operate the engine. The EEC implements a cold start routine, which controls the quantity of fuel injected, the time at which the fuel is injected, and spark timing to achieve a rapid increase in temperature of the engine and the exhaust system components, including a catalytic converter, thereby decreasing hydrocarbon (HC) emissions during cold start. Tomita et al. employs a so-called xe2x80x9cstratified stoichiometric charge combustionxe2x80x9d (S.S.C.C.) by split injection for reduction of tailpipe hydrocarbon emissions and catalyst warm-up time. Upon completion of catalyst warm-up, a switch in combustion mode is made from S.S.C.C. to a so-called xe2x80x9chomogeneous charge combustionxe2x80x9d (H.C.C.).
Fuel injectors utilizing electronic control valves have become widespread. In operation, an energizing or excitation time for the control valve is determined corresponding to current engine conditions. The excitation of the control valve causes the lifting of the spray tip needle, which causes fuel injection to occur. Fuel quantity and pulse width hold linearity when the pulse width exceeds a minimum pulse width (TIMIN) as shown in FIG. 3. This linearity is broken when pulse width is less than the minimum pulse width so that precise control of lower fuel quantities is difficult to achieve. However, precise control over such lower fuel quantities is essential when split-injection is required for S.S.C.C.
In order to achieve precise control over lower fuel quantities unachievable with pulse width only, injection pressure may be reduced and pulse width may be increased. At such reduced injection pressure appropriate for split injection, increased fuel quantity may not be injected only by increasing pulse width, leading to a sluggish response to an increase in torque demand during acceleration or up-hill climbing of vehicle operation.
A spark timing control routine, which controls spark timing to provide smooth torque change, is described in copending U.S. patent application Ser. No. 09/649,995, filed Aug. 29, 2000, assigned to the assignee of the present invention. The spark timing control has proved to be effective in providing smooth change in engine torque at the expense of quick response to an increase in torque demand. As a result, a sluggish response to increased torque demand during acceleration or up-hill climbing of vehicle operation is unavoidable.
It is an object of the present invention to provide a quick response to an increase in torque demand when a spark ignited internal combustion engine operates on S.S.C.C. during operation to warm-up catalyst.
In accordance with a preferred embodiment of the present invention, the primary object of the present invention is solved by a method for enhanced response to operator torque demand in a spark ignited internal combustion engine. The engine has fuel injectors positioned to inject fuel directly into combustion chambers of the engine. The method comprises:
operating the engine on stratified stoichiometry charge combustion (S.S.C.C.), during a predetermined engine operation, by performing a split injection for each engine cycle, and controlling spark timing according to a first ignition timing point;
varying a period of time, which is required for advancing spark timing from the first ignition timing point to a second ignition timing point during switch from S.S.C.C. to H.C.C., with differing degrees of the operator torque demand; and
operating the engine on H.C.C. by performing a single injection for each engine cycle after elapse of said period of time.